If phantomjs-url and phantomjs-url-template are
not specified, you can set a template which will populate various
variables. The variables should be wrapped in {}, and the
following values are supported:

arch: the architecture. x86_64 or i686

phantom_platform: the platform, following the format dictated by the standard phantomjs url (e.g. linux, macosx)

phantom_extension: the extension, as specified by the format dictated by the standard phantomjs url (e.g. tar.bz2, zip)